The present invention relates to novel oligomeric and polymeric condensation products of phosphine oxides, such as bis(p-hydroxyphenyl)alkyl or aryl phosphine oxides condensed with alkyl or arylphosphonic dihalides or diphenoxides. The invention also relates to processes of preparing the present novel compositions of matter. Another embodiment of the invention is a process of imparting fire-retardant properties to combustible materials by treatment with the condensation products of the present invention, as well as novel compositions composed of otherwise combustible base materials such as various organic polymers for example Nylon or polyethylene terephthalate having combined therewith the present condensation products.